Proactive link acquisition (spatial awareness)

ABSTRACT

A system is disclosed. The system may include a receiver or transmitter node. The receiver or transmitter node may include a communications interface with an antenna element and a controller. The controller may include one or more processors and have information of own node velocity and own node orientation relative to a common reference frame. The receiver or transmitter node may be time synchronized to apply Doppler corrections to signals, the Doppler corrections associated with the receiver or transmitter node&#39;s own motions relative to the common reference frame, the Doppler corrections applied using Doppler null steering along Null directions. The receiver node may comprise a correlator configured to process the signals which are based on the Doppler null steering.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims priority from the following U.S. patent applications:

-   -   (a) U.S. patent application Ser. No. 17/233,107, filed Apr. 16,         2021, which is incorporated by reference in its entirety;     -   (b) P.C.T. Patent Application No. PCT/US22/24653, filed Apr. 13,         2022, which claims priority to U.S. patent application Ser. No.         17/233,107, filed Apr. 16, 2021, all of which are incorporated         by reference in its entirety;     -   (c) U.S. patent application Ser. No. 17/408,156, filed Aug. 20,         2021, which claims priority to U.S. patent application Ser. No.         17/233,107, filed Apr. 16, 2021, all of which are incorporated         by reference in its entirety;     -   (d) U.S. patent application Ser. No. 17/541,703, filed Dec. 3,         2021, which is incorporated by reference in its entirety, which         claims priority to:     -   U.S. patent application Ser. No. 17/408,156, filed Aug. 20,         2021, which is incorporated by reference in its entirety; and     -   U.S. patent application Ser. No. 17/233,107, filed Apr. 16,         2021, all of which is incorporated by reference in its entirety;     -   (e) U.S. patent application Ser. No. 17/534,061, filed Nov. 23,         2021, which is incorporated by reference in its entirety;     -   (f) U.S. Patent Application No. 63/344,445, filed May 20, 2022,         which is incorporated by reference in its entirety;     -   (g) U.S. patent application Ser. No. 17/857,920, filed Jul. 5,         2022, which is incorporated by reference in its entirety;     -   (h) U.S. Patent Application No. 63/400,138, filed Aug. 23, 2022,         which is incorporated by reference in its entirety;     -   (i) U.S. patent application Ser. No. 17/940,898, filed Sep. 8,         2022, which is incorporated by reference in its entirety;     -   (j) U.S. patent application Ser. No. 17/941,907, filed Sep. 9,         2022, which is incorporated by reference in its entirety;     -   (k) U.S. patent application Ser. No. 17/957,881, filed Sep. 30,         2022, which is incorporated by reference in its entirety;     -   (l) U.S. patent application Ser. No. 17/990,491, filed Nov. 18,         2022, which is incorporated by reference in its entirety;     -   (m) U.S. patent application Ser. No. 18/130,285, filed Apr. 3,         2023, which is incorporated by reference in its entirety; and     -   (n) U.S. patent application Ser. No. 18/134,950, filed Apr. 14,         2023, which is incorporated by reference in its entirety.

BACKGROUND

The current practice in wireless communication uses lengthy preambles for packet (i.e., message) acquisitions. For example, message acquisitions may use long or complex start of message (SOM) sequences to determine when a message starts. These SOM may require many correlators to process the SOM.

It may be desirable to have a system that overcomes at least some of these limitations.

SUMMARY

A system is disclosed. The system may include a receiver or transmitter node. The receiver or transmitter node may include a communications interface with an antenna element and a controller. The controller may include one or more processors and have information of own node velocity and own node orientation relative to a common reference frame. The receiver or transmitter node may be time synchronized to apply Doppler corrections to signals, the Doppler corrections associated with the receiver or transmitter node's own motions relative to the common reference frame, the Doppler corrections applied using Doppler null steering along Null directions. The receiver node may comprise a correlator configured to process the signals which are based on Doppler null steering.

This Summary is provided solely as an introduction to subject matter that is fully described in the Detailed Description and Drawings. The Summary should not be considered to describe essential features nor be used to determine the scope of the Claims. Moreover, it is to be understood that both the foregoing Summary and the following Detailed Description are example and explanatory only and are not necessarily restrictive of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items. Various embodiments or examples (“examples”) of the present disclosure are disclosed in the following detailed description and the accompanying drawings. The drawings are not necessarily to scale. In general, operations of disclosed processes may be performed in an arbitrary order, unless otherwise provided in the claims.

FIG. 1 is a diagrammatic illustration of two nodes in a simplified mobile network and individual nodes thereof according to example embodiments of this disclosure.

FIG. 2A is a graphical representation of frequency shift profiles within the network of FIG. 1 .

FIG. 2B is a graphical representation of frequency shift profiles within the network of FIG. 1 .

FIG. 3 is a diagrammatic illustration of a transmitter node and a receiver node according to example embodiments of this disclosure.

FIG. 4A is a graphical representation of frequency shift profiles within the network of FIG. 3 .

FIG. 4B is a graphical representation of frequency shift profiles within the network of FIG. 3 .

FIG. 5 is a graph of sets for covering space.

FIG. 6 is a diagrammatic illustration of a transmitter node and a receiver node according to example embodiments of this disclosure.

FIG. 7 is a flow diagram illustrating a method according to example embodiments of this disclosure.

FIG. 8 is a time-based graphical representation of a message acquisition including a start-of-message sequence.

FIG. 9 is a time-based graphical representation of a plurality of pulses with a time period separating the pulses, according to example embodiments of this disclosure.

FIG. 10 is a system including an antenna element and a correlator, according to example embodiments of this disclosure.

DETAILED DESCRIPTION

Before explaining one or more embodiments of the disclosure in detail, it is to be understood that the embodiments are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. In the following detailed description of embodiments, numerous specific details may be set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skill in the art having the benefit of the instant disclosure that the embodiments disclosed herein may be practiced without some of these specific details. In other instances, well-known features may not be described in detail to avoid unnecessarily complicating the instant disclosure.

As used herein a letter following a reference numeral is intended to reference an embodiment of the feature or element that may be similar, but not necessarily identical, to a previously described element or feature bearing the same reference numeral (e.g., 1, 1 a, 1 b). Such shorthand notations are used for purposes of convenience only and should not be construed to limit the disclosure in any way unless expressly stated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of “a” or “an” may be employed to describe elements and components of embodiments disclosed herein. This is done merely for convenience and “a” and “an” are intended to include “one” or “at least one,” and the singular also includes the plural unless it is obvious that it is meant otherwise.

Finally, as used herein any reference to “one embodiment”, “in embodiments” or “some embodiments” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment disclosed herein. The appearances of the phrase “in some embodiments” in various places in the specification are not necessarily all referring to the same embodiment, and embodiments may include one or more of the features expressly described or inherently present herein, or any combination or sub-combination of two or more such features, along with any other features which may not necessarily be expressly described or inherently present in the instant disclosure.

Broadly speaking, embodiments herein are directed to systems and methods for achieving proactive link acquisition.

As described in U.S. patent application Ser. No. 18/130,285, filed Apr. 3, 2023, which is herein incorporated by reference in its entirety, embodiments may utilize time synchronized scanning sequences (along with directionality) to improve metrics such as signal-to-noise ratio, signal acquisition time, speed of attaining situational awareness of attributes of surrounding nodes, range, and the like. In some embodiments, a zero value or near zero value (e.g., or the like such as a zero crossing) of a calculated net frequency shift of a received signal is used to determine a bearing angle between the source (e.g., Tx node) and the receiving node using a time-of-arrival of the received signal. The bearing angle may be made more accurate by combining (e.g., averaging) it with another bearing angle estimation determined from an angle of peak amplitude gain of the signal.

It is noted that U.S. patent application Ser. No. 17/857,920, filed Jul. 5, 2022, is at least partially reproduced by at least some (or all) of the illustrations of FIGS. 1-7 and at least some (or all) of the corresponding language for FIGS. 1-7 below. For example, at least some examples of doppler nulling methods and systems may be better understood, in a nonlimiting manner, by reference to FIGS. 1-7 . Such embodiments and examples are provided for illustrative purposes and are not to be construed as necessarily limiting. For instance, in embodiments the transmitter node may be stationary rather than moving and/or vice versa.

Moreover, and stated for purposes of navigating the disclosure only and not to be construed as limiting, descriptions that may relate to other language not necessarily reproduced from U.S. patent application Ser. No. 17/857,920 include the discussion and figures after FIGS. 1-7 .

Referring now to FIGS. 1-7 , in some embodiments, a stationary receiver may determine a cooperative transmitter's direction and velocity vector by using a Doppler null scanning approach in two dimensions. A benefit of the approach is the spatial awareness without exchanging explicit positional information. Other benefits include discovery, synchronization, and Doppler corrections which are important for communications. Some embodiment may combine coordinated transmitter frequency shifts along with the transmitter's motion induced Doppler frequency shift to produce unique net frequency shift signal characteristics resolvable using a stationary receiver to achieve spatial awareness. Further, some embodiment may include a three-dimensional (3D) approach with the receiver and the transmitter in motion.

Some embodiments may use analysis performed in a common reference frame (e.g., a common inertial reference frame, such as the Earth, which may ignore the curvature of Earth), and it is assumed that the communications system for each of the transmitter and receiver is informed by the platform of its own velocity and orientation. The approach described herein can be used for discovery and tracking, but the discussion here focuses on discovery which is often the most challenging aspect.

The meaning of the ‘Doppler Null’ can be explained in part through a review of the two-dimensional (2D) case without the receiver motion, and then may be expounded on by a review of adding the receiver motion to the 2D case, and then including receiver motion in the 3D case.

The Doppler frequency shift of a communications signal is proportional to the radial velocity between transmitter and receiver, and any significant Doppler shift is typically a hindrance that should be considered by system designers. In contrast, some embodiments utilize the Doppler effect to discriminate between directions with the resolution dictated by selected design parameters. Furthermore, such embodiments use the profile of the net frequency shift as the predetermined ‘Null’ direction scans through the angle space. The resultant profile is sinusoidal with an amplitude that provides the transmitter's speed, a zero net frequency shift when the ‘Null’ direction aligns with the receiver, and a minimum indicating the direction of the transmitter's velocity. It should be noted that that the transmitter cannot correct for Doppler in all directions at one time so signal characteristics are different in each direction and are different for different transmitter velocities as well. It is exactly these characteristics that the receiver uses to determine spatial awareness. The received signal has temporal spatial characteristics that can be mapped to the transmitter's direction and velocity. This approach utilizes the concept of a ‘Null’ which is simply the direction where the transmitter perfectly corrects for its own Doppler shift. The same ‘Nulling’ protocol runs on each node and scans through all directions, such as via a scanning sequence of a protocol. Here we arbitrarily illustrate the scanning with discrete successive steps of 10 degrees but in a real system; however, it should be understood that any suitable step size of degrees may be used for Doppler null scanning.

As already mentioned, one of the contributions of some embodiments is passive spatial awareness. Traditionally, spatial information for neighbor nodes (based on a global positioning system (GPS) and/or gyros and accelerometers) can be learned via data communication. Unfortunately, spatial awareness via data communication, referred to as active spatial awareness is possible only after communication has already been established, not while discovering those neighbor nodes. Data communication is only possible after the signals for neighbor nodes have been discovered, synchronized and Doppler corrected. In contrast, in some embodiments, the passive spatial awareness described herein may be performed using only synchronization bits associated with acquisition. This process can be viewed as physical layer overhead and typically requires much lower bandwidth compared to explicit data transfers. The physical layer overheads for discovery, synchronization and Doppler correction have never been utilized for topology learning for upper layers previously.

Traditionally, network topology is harvested via a series of data packet exchanges (e.g., hello messaging and link status advertisements). The passive spatial awareness may eliminate hello messaging completely and provide a wider local topology which is beyond the coverage of hello messaging. By utilizing passive spatial awareness, highly efficient mobile ad hoc networking is possible. Embodiments may improve the functioning of a network, itself.

Referring to FIG. 1 , a multi-node communications network 100 is disclosed. The multi-node communications network 100 may include multiple communications nodes, e.g., a transmitter (Tx) node 102 and a receiver (Rx) node 104.

In embodiments, the multi-node communications network 100 may include any multi-node communications network known in the art. For example, the multi-node communications network 100 may include a mobile network in which the Tx and Rx nodes 102, 104 (as well as every other communications node within the multi-node communications network) is able to move freely and independently. Similarly, the Tx and Rx nodes 102, 104 may include any communications node known in the art which may be communicatively coupled. In this regard, the Tx and Rx nodes 102, 104 may include any communications node known in the art for transmitting/transceiving data packets. For example, the Tx and Rx nodes 102, 104 may include, but are not limited to, radios (such as on a vehicle or on a person), mobile phones, smart phones, tablets, smart watches, laptops, and the like. In embodiments, the Rx node 104 of the multi-node communications network 100 may each include, but are not limited to, a respective controller 106 (e.g., control processor), memory 108, communication interface 110, and antenna elements 112. (In embodiments, all attributes, capabilities, etc. of the Rx node 104 described below may similarly apply to the Tx node 102, and to any other communication node of the multi-node communication network 100.)

In embodiments, the controller 106 provides processing functionality for at least the Rx node 104 and can include any number of processors, micro-controllers, circuitry, field programmable gate array (FPGA) or other processing systems, and resident or external memory for storing data, executable code, and other information accessed or generated by the Rx node 104. The controller 106 can execute one or more software programs embodied in a non-transitory computer readable medium (e.g., memory 108) that implement techniques described herein. The controller 106 is not limited by the materials from which it is formed or the processing mechanisms employed therein and, as such, can be implemented via semiconductor(s) and/or transistors (e.g., using electronic integrated circuit (IC) components), and so forth.

In embodiments, the memory 108 can be an example of tangible, computer-readable storage medium that provides storage functionality to store various data and/or program code associated with operation of the Rx node 104 and/or controller 106, such as software programs and/or code segments, or other data to instruct the controller 106, and possibly other components of the Rx node 104, to perform the functionality described herein. Thus, the memory 108 can store data, such as a program of instructions for operating the Rx node 104, including its components (e.g., controller 106, communication interface 110, antenna elements 112, etc.), and so forth. It should be noted that while a single memory 108 is described, a wide variety of types and combinations of memory (e.g., tangible, non-transitory memory) can be employed. The memory 108 can be integral with the controller 106, can comprise stand-alone memory, or can be a combination of both. Some examples of the memory 108 can include removable and non-removable memory components, such as random-access memory (RAM), read-only memory (ROM), flash memory (e.g., a secure digital (SD) memory card, a mini-SD memory card, and/or a micro-SD memory card), solid-state drive (SSD) memory, magnetic memory, optical memory, universal serial bus (USB) memory devices, hard disk memory, external memory, and so forth.

In embodiments, the communication interface 110 can be operatively configured to communicate with components of the Rx node 104. For example, the communication interface 110 can be configured to retrieve data from the controller 106 or other devices (e.g., the Tx node 102 and/or other nodes), transmit data for storage in the memory 108, retrieve data from storage in the memory, and so forth. The communication interface 110 can also be communicatively coupled with the controller 106 to facilitate data transfer between components of the Rx node 104 and the controller 106. It should be noted that while the communication interface 110 is described as a component of the Rx node 104, one or more components of the communication interface 110 can be implemented as external components communicatively coupled to the Rx node 104 via a wired and/or wireless connection. The Rx node 104 can also include and/or connect to one or more input/output (I/O) devices. In embodiments, the communication interface 110 includes or is coupled to a transmitter, receiver, transceiver, physical connection interface, or any combination thereof.

It is contemplated herein that the communication interface 110 of the Rx node 104 may be configured to communicatively couple to additional communication interfaces 110 of additional communications nodes (e.g., the Tx node 102) of the multi-node communications network 100 using any wireless communication techniques known in the art including, but not limited to, GSM, GPRS, CDMA, EV-DO, EDGE, WiMAX, 3G, 4G, 4G LTE, 5G, WiFi protocols, RF, LoRa, and the like.

In embodiments, the antenna elements 112 may include directional or omnidirectional antenna elements capable of being steered or otherwise directed (e.g., via the communications interface 110) for spatial scanning in a full 360-degree arc (114) relative to the Rx node 104 (or even less than a full 360 degree arc).

In embodiments, the Tx node 102 and Rx node 104 may one or both be moving in an arbitrary direction at an arbitrary speed, and may similarly be moving relative to each other. For example, the Tx node 102 may be moving relative to the Rx node 104 according to a velocity vector 116, at a relative velocity V_(Tx) and a relative angular direction (an angle α relative to an arbitrary direction 118 (e.g., due east); θ may be the angular direction of the Rx node relative to due east.

In embodiments, the Tx node 102 may implement a Doppler nulling protocol. For example, the Tx node 102 may adjust its transmit frequency to counter the Doppler frequency offset such that there is no net frequency offset (e.g., “Doppler null”) in a Doppler nulling direction 120 (e.g., at an angle ϕ relative to the arbitrary direction 118). The transmitting waveform (e.g., the communications interface 110 of the Tx node 102) may be informed by the platform (e.g., the controller 106) of its velocity vector and orientation (e.g., α, V_(T)) and may adjust its transmitting frequency to remove the Doppler frequency shift at each Doppler nulling direction 120 and angle ϕ.

To illustrate aspects of some embodiments, we show the 2D dependence of the net frequency shift for a stationary receiver as a function of Null direction across the horizon, as shown in a top-down view of FIG. 1 , where the receiver node 104 is stationary and positioned θ from east relative to the transmitter, the transmitter node 102 is moving with a speed |

| and direction a from east and a snapshot of the scanning ϕ which is the ‘Null’ direction, exemplarily shown as 100 degrees in this picture.

The Doppler shift is a physical phenomenon due to motion and can be considered as a channel effect. In this example the transmitter node 102 is the only moving object, so it is the only source of Doppler shift. The Doppler frequency shift as seen by the receiver node 104 due to the transmitter node 102 motion is:

${\frac{\Delta f_{DOPPLER}}{f} = {\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}}},$

where c is the speed of light

The other factor is the transmitter frequency adjustment term that should exactly compensate the Doppler shift when the ‘Null’ direction aligns with the receiver direction. It is the job of the transmitter node 102 to adjust its transmit frequency according to its own speed (|{right arrow over (V_(T))}|), and velocity direction (α). That transmitter frequency adjustment (Δf_(T)) is proportional to the velocity projection onto the ‘Null’ direction (Φ) and is:

$\frac{\Delta f_{T}}{f} = {{- \frac{❘\overset{\rightarrow}{V_{T}}❘}{c}}{\cos\left( {\varphi - \alpha} \right)}}$

The net frequency shift seen by the receiver is the sum of the two terms:

$\frac{\Delta f_{net}}{f} = {\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack}$

It is assumed that the velocity vector and the direction changes slowly compared to the periodic measurement of Δf_(net). Under those conditions, the unknown parameters (from the perspective of the receiver node 104) of α, |{right arrow over (V_(T))}|, and θ are constants.

Furthermore, it is assumed that the receiver node 104 has an implementation that resolves the frequency of the incoming signal, as would be understood to one of ordinary skill in the art.

FIG. 2A shows the resulting net frequency shift as a function of the ‘Null’ direction for scenarios where a stationary receiver is East of the transmitter (theta=0), and with a transmitter speed of 1500 meters per second (m/s). FIG. 2B shows the results for a stationary receiver and for several directions with an Eastern transmitter node velocity direction (alpha=0). The frequency shifts are in units of parts per million (ppm). As shown in FIGS. 2A and 2B, the amplitude is consistent with the transmitter node's 102 speed of 5 ppm [|{right arrow over (V_(T))}|/c*(1×10⁶)] regardless of the velocity direction or position, the net frequency shift is zero when the ‘Null’ angle is in the receiver direction (when ϕ=θ), and the minimum occurs when the ‘Null’ is aligned with the transmitter node's 102 velocity direction (when ϕ=α).

From the profile, the receiver node 104 can therefore determine the transmitter node's 102 speed, the transmitter node's 102 heading, and the direction of the transmitter node 102 is known to at most, one of two locations (since some profiles have two zero crossings). It should be noted that the two curves cross the y axis twice (0 & 180 degrees in FIG. 2A, and ±90 degrees in FIG. 2B) so there is initially an instance of ambiguity in position direction. In this case the receiver node 104 knows the transmitter node 102 is either East or West of the receiver node 104.

Referring to FIG. 3 , a multi-node communications network 100 is disclosed. The multi-node communications network 100 may include multiple communications nodes, e.g., a transmitter (Tx) node 102 and a receiver (Rx) node 104. As shown in FIG. 3 both of the transmitter node 102 and the receiver node 104 are in motion in two dimensions.

The simultaneous movement scenario is depicted in FIG. 3 where the receiver node 104 is also moving in a generic velocity characterized by a speed |

| and the direction, β. The protocol for the moving receiver node 104 incorporates a frequency adjustment on the receiver node's 104 side to compensate for the receiver node's 104 motion as well. The equations have two additional terms. One is a Doppler term for the motion of the receiver and the second is frequency compensation by the receiver.

Again, the Doppler shift is a physical phenomenon due to motion and can be considered as a channel effect, but in this case both the transmitter node 102 and the receiver node 104 are moving so there are two Doppler shift terms. The true Doppler shift as seen by the receiver due to the relative radial velocity is:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}} - {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}{\cos\left( {\theta - \beta} \right)}}}$

The other factors are the transmitter node 102 and receiver node 104 frequency adjustment terms that exactly compensates the Doppler shift when the ‘Null’ direction aligns with the receiver direction. It is the job of the transmitter node 102 to adjust the transmitter node's 102 transmit frequency according to its own speed (|{right arrow over (V_(T))}|), and velocity direction (α). That transmitter node frequency adjustment is proportional to the velocity projection onto the ‘Null’ direction (Φ) and is the first term in the equation below.

It is the job of the receiver node 104 to adjust the receiver node frequency according to the receiver node's 104 own speed (|{right arrow over (V_(R))}|), and velocity direction (β). That receiver node frequency adjustment is proportional to the velocity projection onto the ‘Null’ direction (

) and is the second term in the equation below. The receiver node frequency adjustment can be done to the receive signal prior to the frequency resolving algorithm or could be done within the algorithm.

$\frac{\Delta f_{{T\&}R}}{f} = {{{- \frac{❘\overset{\rightarrow}{V_{T}}❘}{c}}{\cos\left( {\varphi - \alpha} \right)}} + {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}{\cos\left( {\varphi - \beta} \right)}}}$

The net frequency shift seen by the receiver is the sum of all terms:

$\frac{\Delta f_{net}}{f} = {{\frac{❘\overset{\rightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack} - {\frac{❘\overset{\rightarrow}{V_{R}}❘}{c}\left\lbrack {{\cos\left( {\theta - \beta} \right)} - {\cos\left( {\varphi - \beta} \right)}} \right\rbrack}}$

Again, it is assumed that the receiver node 104 has an implementation that resolves the frequency of the incoming signal, as would be understood in the art.

Also, it is assumed that the velocity vector and direction changes slowly compared to the periodic measurement of Δf_(net). Again, under such conditions, the unknown parameters (from the perspective of the receiver node 104) α, |{right arrow over (V_(T))}|, and θ are constants. When the velocity vector or direction change faster, then this change could be tracked, for example if the change is due to slow changes in acceleration.

The net frequency shift for the two-dimensional (2D) moving receiver node 104 approach is shown in FIGS. 4A and 4B for several scenario cases of receiver node location, θ, and transmitter node and receiver node speeds (|{right arrow over (V_(T))}| & |{right arrow over (V_(R))}|), as well as transmitter node and receiver node velocity direction (α and β). FIG. 4A has different speeds for the transmitter node 102 and receiver node 104 as well as the receiver node location of θ=0. FIG. 4B has the same speed for the transmitter node and receiver node. Similarly, there are three concepts to notice here:

-   -   The amplitude is consistent with the relative velocity between         transmitter node 102 and receiver node 104 [|(|{right arrow over         (V_(T))}| cos (α)−|{right arrow over (V_(R))}| cos (β))|/c         *(1e6)].     -   The net frequency shift is zero when the ‘Null’ angle is in the         receiver direction (when ϕ=θ).     -   The minimum occurs when the ‘Null’ is aligned with the relative         velocity direction (when ϕ=angle(|{right arrow over (V_(T))}|         cos (α)−|{right arrow over (V_(R))}| cos (β))).

Again, there is an initial dual point ambiguity with the position, θ, but the transmitter node's 102 speed and velocity vector is known.

Referring now to FIG. 5 , while the 2D picture is easier to visualize, the same principles apply to the 3D case. FIG. 5 shows a number of direction sets needed to span 3D and 2D space with different cone sizes (cone sizes are full width). Before diving into the equations, it's worth commenting on the size of the space when including another dimension. For example, when a ‘Null’ step size of 10 degrees was used in the previous examples, it took 36 sets to span the 360 degrees in 2D. Thus, if an exemplary detection angle of 10 degrees is used (e.g., a directional antenna with 10-degree cone) it would take 36 sets to cover the 2D space. The 3D fractional coverage can be computed by calculating the coverage of a cone compared to the full 4 pi steradians. The fraction is equal to the integral

${{FractionCoverage}3D} = {\frac{\int_{0}^{{ConeSize}/2}{r^{2}{\sin\left( \theta^{\prime} \right)}d\theta^{\prime}d\varphi}}{4\pi r^{2}} = \frac{1 - {\cos\left( {{ConeSize}/2} \right)}}{2}}$ FractionCoverage2D = 2π/ConeSize

The number of sets to span the space is shown in FIG. 5 for both the 2D and 3D cases which correlates with discovery time. Except for narrow cone sizes, the number of sets is not drastically greater for the 3D case (e.g., approximately 15 times at 10 degrees, 7 time at 20 degrees, and around 5 times at 30 degrees). Unless systems are limited to very narrow cone sizes, the discovery time for 3D searches is not overwhelming compared to a 2D search.

Referring now to FIG. 6 , a multi-node communications network 100 is disclosed. The multi-node communications network 100 may include multiple communications nodes, e.g., a transmitter (Tx) node 102 and a receiver (Rx) node 104. As shown in FIG. 6 both of the transmitter node 102 and the receiver node 104 are in motion in three dimensions.

The 3D approach to Doppler nulling follows the 2D approach but it is illustrated here with angles and computed vectorially for simplicity.

In three dimensions, it is convenient to express the equations in vector form which is valid for 2 or 3 dimensions. FIG. 6 shows the geometry in 3 dimensions where

is the unit vector pointing to the receiver from the transmitter, and

is the unit vector pointing in the ‘Null’ direction defined by the protocol.

The true Doppler shift as seen by the receiver node 104 due to the relative radial velocity which is the projection onto the

vector:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The nulling protocol adjusts the transmit node frequency and receiver node frequency due to their velocity projections onto the

direction

$\frac{\Delta f_{T}}{f} = {{{- \frac{1}{c}}{\overset{\rightarrow}{V_{T}} \cdot}} + {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The net frequency shift seen by the receiver node 104 is the sum of all terms:

$\frac{\Delta f_{net}}{f} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} + {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}$

The net frequency shift for the 3D moving receiver node 104 approach is not easy to show pictorially but can be inspected with mathematical equations to arrive at useful conclusions. The first two terms are the Doppler correction (DC) offset and the last two terms are the null dependent terms. Since the

is the independent variable, the maximum occurs when ({right arrow over (V_(R))}−{right arrow over (V_(T))}) and

are parallel and is a minimum when they are antiparallel. Furthermore, the relative speed is determined by the amplitude,

${Amplitude} = {\frac{1}{c}{❘{\overset{\rightarrow}{V_{R}} - \overset{\rightarrow}{V_{T}}}❘}}$

Lastly, the net frequency is zero when the

is parallel (i.e., parallel in same direction, as opposed to anti-parallel) to

.

${\frac{\Delta f_{net}}{f} = {0{when}}},{{{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}} = {{\frac{1}{c}{\overset{\rightarrow}{V_{T}} \cdot}} - {\frac{1}{c}{\overset{\rightarrow}{V_{R}} \cdot}}}}$ ${or},{{\left( {{\overset{\rightarrow}{V}}_{T} - {\overset{\rightarrow}{V}}_{R}} \right) \cdot} = {\left( {{\overset{\rightarrow}{V}}_{T} - {\overset{\rightarrow}{V}}_{R}} \right) \cdot}}$

For the 3D case:

-   -   The amplitude is consistent with the relative velocity between         transmitter node 102 and receiver node 104 [|{right arrow over         (V_(R))}−{right arrow over (V_(T))}|/c].     -   The net frequency shift is zero when the ‘Null’ angle is in the         receiver node direction, ({right arrow over (V_(T))}−{right         arrow over (V_(R))})·         ({right arrow over (V_(T))}−{right arrow over (V_(R))})·         ).     -   The minimum occurs when the ‘Null’ is aligned with the relative         velocity direction.

Referring still to FIG. 6 , in some embodiments, the system (e.g., the multi-node communications network 100) may include a transmitter node 102 and a receiver node 104. Each node of the transmitter node 102 and the receiver node 104 may include a communications interface 110 including at least one antenna element 112 and a controller operatively coupled to the communications interface, the controller 106 including one or more processors, wherein the controller 106 has information of own node velocity and own node orientation. The transmitter node 102 and the receiver node 104 may be in motion (e.g., in two dimensions or in three dimensions). The transmitter node 102 and the receiver node 104 may be time synchronized to apply Doppler corrections associated with said node's own motions relative to a common reference frame (e.g., a common inertial reference frame (e.g., a common inertial reference frame in motion or a stationary common inertial reference frame)). The common reference frame may be known to the transmitter node 102 and the receiver node 104 prior to the transmitter node 102 transmitting signals to the receiver node 104 and prior to the receiver node 104 receiving the signals from the transmitter node 102. In some embodiments, the system is a mobile network comprising the transmitter node 102 and the receiver node 104.

In some embodiments, the applying of the Doppler corrections associated with the receiver node's own motions relative to the common reference frame is based on a common reference frequency. For example, a common reference frequency may be adjusted by a node's own motions to cancel out those motions in reference to the null angle. This common reference frequency may be known by each node prior to transmission and/or reception of the signals. In some embodiments, calculating the net frequency change seen by the receiver node 104 is based on the common reference frequency. For example, the net frequency change may be a difference between a measured frequency of the signals and the common reference frequency.

For purposes of discussing the receiver node 104, a “source” generally refers to a source of a received signal, multiple sources of multiple signals, a single source of multiple signals, and/or the like. For example, a source may be a transmitter node 102 configured to apply Doppler corrections as disclosed herein and in applications from which priority is claimed and/or incorporated by reference. In this regard, a receiver node 104 may determine one or more attributes of the source (e.g., bearing between the receiver node 104 and the source, bearing of the velocity of the source, amplitude/speed of the velocity, range, and the like). In some embodiments, the receiver node 104 and the source (e.g., transmitter node 102) are configured to use a same, compatible, and/or similar Doppler correction, protocol, common reference frame, common reference frequency, time synchronization, and/or the like such that the receiver node 104 may determine various attributes of the source. Note, in some embodiments, that one or more of these may be known ahead of time, be determined thereafter, included as fixed variable values as part of the protocol, and/or determined dynamically (in real time) as part of the protocol. For example, the protocol may determine that certain common reference frames should be used in certain environments, such as using GPS coordinates on land and a naval ship beacon transmitter common reference frame location (which may be mobile) over certain areas of ocean, which may dynamically change in real time as a location of a node changes.

In some embodiments, the transmitter node 102 and the receiver node 104 are time synchronized via synchronization bits associated with acquisition. For example, the synchronization bits may operate as physical layer overhead.

In some embodiments, the transmitter node 102 is configured to adjust a transmit frequency according to an own speed and an own velocity direction of the transmitter node 102 so as to perform a transmitter-side Doppler correction. In some embodiments, the receiver node 104 is configured to adjust a receiver frequency of the receiver node 104 according to an own speed and an own velocity direction of the receiver node 104 so as to perform a receiver-side Doppler correction. In some embodiments, an amount of adjustment of the adjusted transmit frequency is proportional to a transmitter node 102 velocity projection onto a Doppler null direction, wherein an amount of adjustment of the adjusted receiver frequency is proportional to a receiver node 104 velocity projection onto the Doppler null direction. In some embodiments, the receiver node 102 is configured to determine a relative speed between the transmitter node 102 and the receiver node 104. In some embodiments, the receiver node 104 is configured to determine a direction that the transmitter node 102 is in motion and a velocity vector of the transmitter node 102. In some embodiments, a maximum net frequency shift for a Doppler correction by the receiver node 104 occurs when a resultant vector is parallel to the Doppler null direction, wherein the resultant vector is equal to a velocity vector of the receiver node 104 minus the velocity vector of the transmitter node 102. In some embodiments, a minimum net frequency shift for a Doppler correction by the receiver node 104 occurs when a resultant vector is antiparallel to the Doppler null direction, wherein the resultant vector is equal to a velocity vector of the receiver node 104 minus the velocity vector of the transmitter node 102. In some embodiments, a net frequency shift for a Doppler correction by the receiver node 104 is zero when a vector pointing to the receiver node from the transmitter node 102 is parallel to the Doppler null direction.

Referring now to FIG. 7 , an exemplary embodiment of a method 700 according to the inventive concepts disclosed herein may include one or more of the following steps. Additionally, for example, some embodiments may include performing one or more instances of the method 700 iteratively, concurrently, and/or sequentially. Additionally, for example, at least some of the steps of the method 700 may be performed in parallel and/or concurrently. Additionally, in some embodiments, at least some of the steps of the method 700 may be performed non-sequentially.

A step 702 may include providing a transmitter node and a receiver node, wherein each node of the transmitter node and the receiver node are time synchronized, wherein each node of the transmitter node and the receiver node are in motion, wherein each node of the transmitter node and the receiver node comprises a communications interface including at least one antenna element, wherein each node of the transmitter node and the receiver node further comprises a controller operatively coupled to the communications interface, the controller including one or more processors, wherein the controller has information of own node velocity and own node orientation.

A step 704 may include based at least on the time synchronization, applying, by the transmitter node, Doppler corrections to the transmitter node's own motions relative to a common reference frame.

A step 706 may include based at least on the time synchronization, applying, by the receiver node, Doppler corrections to the receiver node's own motions relative to the common reference frame, wherein the common reference frame is known to the transmitter node and the receiver node prior to the transmitter node transmitting signals to the receiver node and prior to the receiver node receiving the signals from the transmitter node.

Further, the method 700 may include any of the operations disclosed throughout.

The null scanning technique discussed herein illustrates a system and a method for spatial awareness from resolving the temporal spatial characteristics of the transmitter node's 102 radiation. This approach informs the receiver node 104 of the relative speed between the transmitter node 102 and receiver node 104 as well as the transmitter node direction and transmitter node velocity vector. This approach includes scanning through all directions and has a high sensitivity (e.g., low net frequency shift) when the null direction is aligned with the transmitter node direction. This approach can be implemented on a highly sensitive acquisition frame which is typically much more sensitive than explicit data transfers which allow for the ultra-sensitive spatial awareness with relatively low power.

This sentence may mark an end to the (at least partially) reproduced language from U.S. patent application Ser. No. 17/857,920 corresponding to the (at least partially) reproduced FIGS. 1-7 . However, note that this paragraph is nonlimiting, and changes may have been made and language added or removed, and not all the language above or corresponding figures above are necessarily reproduced from U.S. patent application Ser. No. 17/857,920.

Directional doppler nulling may be an enabling technology for reducing discovery time within directional networks, thereby allowing for improvement in other performance metrics as well. Because of the significantly improved discovery time, directional Doppler-nulling may also be enabling technology for low-probability of detection (LPD) directional networks.

Examples of doppler nulling methods include, but are not limited to, methods and other descriptions (e.g., at least some theory and mathematical basis) are disclosed in U.S. patent application Ser. No. 17/233,107, filed Apr. 16, 2021, which is hereby incorporated by reference in its entirety; U.S. patent application Ser. No. 17/534,061, filed Nov. 23, 2021, which is hereby incorporated by reference in its entirety; and U.S. patent application Ser. No. 17/857,920, filed Jul. 5, 2022, which is hereby incorporated by reference in its entirety. In embodiments, doppler nulling methods allow for benefits such as, but not limited to, relatively quickly and/or efficiently detecting transmitter nodes and determining transmitter node attributes (e.g., transmitter node speed, transmitter node bearing, relative bearing of transmitter node relative to receiver node, relative distance of transmitter node relative to receiver node, and the like).

Embodiments of the present disclosure may utilize doppler nulling for proactive link acquisition. For example, for some embodiments with doppler nulling, link acquisitions between neighbor nodes can be done prior to the actual explicit data communications because the discovery, synchronization and Doppler corrections (which may be necessary for packet acquisition) are resolved by doppler nulling prior to the packet communication. This may be called ‘proactive link acquisition’ (PLA). With PLA, packet acquisitions are faster with shorter preambles and/or deeper in noise.

In some embodiments herein, a doppler nulling based acquisition approach that separates messages (e.g., pulses) by a time period spacing between the messages allows for a relatively more efficient way to process/acquire messages. For example, such a method may be more efficient compared to using traditional start of message (SOM) indicators requiring multiple correlators. In some embodiments, due to the nature of doppler nulling (e.g., long range discovery, operation in high noise environments, long repetitive sequences being easier to identify in high noise), discovery and synchronization may be obtained using doppler nulling relatively quickly such as almost immediately from the signals. Since SOM indicators are often used to allow two nodes to be synchronized to identify messages, if discovery and synchronization already are achieved via doppler nulling, then doppler nulling may allow for removing unnecessary parts of messages as well as the components and processes needed to analyze those parts of the messages. In this regard, doppler nulling (with discovery and synchronization) may allow for proactive link acquisition. In some examples, proactive link acquisition may allow for removing the need for complex SOM indicators, improving efficiency of systems such as reducing the number of needed correlations/correlators.

Generally, proactive link acquisition is a process including characterizing parameters of each link necessary for communication prior to usage. These parameters may include the arrival time (i.e., different from the nominal transmit time by the combined propagation delay and clock time differences) as well as the signal frequency offset (i.e., different from the nominal center common reference frequency by the combined Doppler shift and clock frequency differences). Knowledge of the above parameters as well as the transmission time (e.g., assumed to be known based on waveform design) is sufficient to determine SOM whereas more traditional message acquisition typically have front heavy acquisition sequences that require multiple simultaneous correlators. Typically, for low signal to noise (SNR) modes, acquisition resource utilization is a practical limitation for communication systems.

Applying doppler nulling to acquisition of messages may allow for reduced need for correlators.

To understand the correlator reuse gains it's helpful to compare a (doppler nulling based) link acquisition approach to a (alternative) message acquisition approach. In general, acquisition requires a certain amount of integrated signal energy. At low signal levels acquisition requires a significant integration time. For many message acquisition systems, the message acquisition acts as a SOM indicator triggering a processing of packets. The SOM typically involves a high concentration of acquisition sequences at the front of the message. Therefore, processing the SOM typically requires multiple simultaneous correlator instances.

By contrast, a (doppler nulling based) link acquisition approach does not necessarily need to indicate ‘start of message’ and therefore can be designed with the multiple pulses separated by more than the maximum propagation time allowing one correlator to process all pulses in the frame. For a 16-pulse acquisition frame this leads to a reduction in correlator resource by 16 over a front-end heavy message acquisition approach.

With similar resource utilization, link acquisition sensitivities can be significantly better due to the above-mentioned correlator reuse, as well as improvement from long sequence utilization with known frequency offset.

FIG. 8 is a time-based graphical representation 800 of a message acquisition including a start-of-message sequence 802 and other message pulses 804. As shown, the start-of-message sequence 802 is included in each frame, with four frames total, so that the start of each frame may be identified and the messages acquired (e.g., identified, processed, recorded, decoded, and/or the like). The start-of-message sequences 802 typically require many correlators. For example, for the graphical representation 800 shown, 16 correlators may be needed.

FIG. 9 is a time-based graphical representation 900 of a plurality of pulses 902 with a time period 906 separating the pulses 902 (e.g., doppler nulling based pulses 902), according to example embodiments of this disclosure.

As shown, no start-of-message sequences 802 are necessarily needed as described above. Each pulse 902 of a frame may be separated by a pulse period 904 and a group of pulses (e.g., frame) may be separated by a time period 906 configured to be used to process the signals including the pulses 902. For example, the time period 906 may be a predetermined time period 906 configured to be known by the transmitter node and the receiver node prior to the transmission of the signals. For instance, known via a protocol that determines the time period 906.

FIG. 10 is a system 100 (e.g., receiver node 102 and/or transmitter node 104) including an antenna element 112 and a correlator 1002 to process a signal (e.g., signal 900, which may be based on a doppler nulling method), according to example embodiments of this disclosure. For example, each receiver node 102 and/or transmitter node 104 may include a single correlator 1002 to acquire the pulses 902.

In some embodiments, the correlator 1002 is configured to process/acquire the pulses 902 based on the time period 906 separating the pulses. For example, the correlator may identify that the time period 906 between each group of pulses 902 indicates a start of a message, where the message includes the group of pulses 902. In this regard, a SOM indicator 802 is not necessarily needed and the number of correlators 1002 may be reduced.

In embodiments, the transmitter node 102 is configured to acquire a link to the receiver node 104 based on the processing of the pulses 902 via the correlator 1002. For example, the transmitter node 102 may establish a two-way explicit data transfer link (e.g., WiFi, Bluetooth, or any other two-way explicit data transfer link known in the art) based on pulses 902. For example, the pulses 902 may be indicative of parameters (e.g., protocol parameters such as frequency, channel, modulations, and the like used to establish such links) of a two-way explicit data transfer link. In this regard, the doppler nulling pulses 902 may allow for a fast establishment of a higher bandwidth two-way explicit data transfer signal.

In embodiments, the pulses 902 may be encoded with information using pulse position modulation. For example, the time of transmission of a group/frame of pulses 902 may be modulated and/or the pulse period 904 between two individual pulses 902 in the same group/frame may be modulated to encode information. For example, an base/center value of the time period 906 may be set by a protocol and if the actual received time period 906 varies by an amount, that amount may be translated into a bit, byte, or the like of information. For example, a 5% increase in the time period 906 and/or pulse period 904 may correspond to a bit value of 1 and a 5% decrease may correspond to bit value of 0. In this regard, doppler nulling with pulse position modulation may allow for encoding explicit data into the signals of pulses 902.

In some embodiments, the signals of pulses 902 are based on a common reference frequency, where the receiver node 104 and the transmitter node 102 are configured to know the common reference frequency prior to the transmitting of the signals. For example, a protocol may set what the common reference frequency is for doppler nulling signals sent by a transmitter node 102, allowing for the receiver node 104 to more easily identify the signals (and nodes) when performing discovery.

For at least purposes of this disclosure, ‘Doppler nulling’ means ‘Doppler null steering’, ‘Doppler null scanning’, and the like.

It is to be understood that embodiments of the methods disclosed herein may include one or more of the steps described herein. Further, such steps may be carried out in any desired order and two or more of the steps may be carried out simultaneously with one another. Two or more of the steps disclosed herein may be combined in a single step, and in some embodiments, one or more of the steps may be carried out as two or more sub-steps. Further, other steps or sub-steps may be carried in addition to, or as substitutes to one or more of the steps disclosed herein.

Although inventive concepts have been described with reference to the embodiments illustrated in the attached drawing figures, equivalents may be employed and substitutions made herein without departing from the scope of the claims. Components illustrated and described herein are merely examples of a system/device and components that may be used to implement embodiments of the inventive concepts and may be replaced with other devices and components without departing from the scope of the claims. Furthermore, any dimensions, degrees, and/or numerical ranges provided herein are to be understood as non-limiting examples unless otherwise specified in the claims. 

We claim:
 1. A system comprising: a transmitter node and a receiver node, wherein each node of the transmitter node and the receiver node comprises: a communications interface comprising at least one antenna element; and a controller operatively coupled to the communications interface, the controller including one or more processors, wherein the controller has information of own node velocity and own node orientation; wherein each node of the transmitter node and the receiver node are in motion relative to each other, wherein each node of the transmitter node and the receiver node are time synchronized to apply Doppler corrections associated with said node's own motions relative to a common reference frame, wherein the transmitter node is configured to apply the Doppler corrections to signals using Doppler null steering along a plurality of Null directions based on the transmitter node's own motions, wherein the common reference frame is known to the transmitter node and the receiver node prior to the transmitter node transmitting the signals to the receiver node and prior to the receiver node receiving the signals from the transmitter node, wherein the receiver node comprises a correlator configured to process pulses of the signals.
 2. The system of claim 1, wherein the correlator is configured to process the pulses based on a discovery of the transmitter node, wherein the discovery is based on the signals which are based on the Doppler null steering.
 3. The system of claim 1, wherein the correlator is configured to process the pulses based on the time synchronization, wherein the time synchronization is based on the signals which are based on the Doppler null steering.
 4. The system of claim 1, wherein the correlator is configured to process the pulses based on a time period separating the pulses.
 5. The system of claim 4, wherein the time period is a predetermined time period configured to be known by the transmitter node and the receiver node prior to the transmission of the signals.
 6. The system of claim 1, wherein the correlator is a single correlator.
 7. The system of claim 1, wherein the transmitter node is configured to acquire a link to the receiver node based on the processing of the pulses via the correlator.
 8. A system comprising: a receiver node comprising: a communications interface comprising at least one antenna element; and a controller operatively coupled to the communications interface, the controller including one or more processors, wherein the controller has information of own node velocity and own node orientation relative to a common reference frame; wherein the receiver node is time synchronized to apply Doppler corrections associated with the receiver node's own motions relative to the common reference frame, wherein the common reference frame is known to the receiver node prior to the receiver node receiving signals from a transmitter node, wherein the receiver node is configured to process the signals according to the Doppler corrections to the signals applied using Doppler null steering along a plurality of Null directions based on the transmitter node's own motions, wherein the receiver node comprises a correlator configured to process pulses of the signals.
 9. The system of claim 8, wherein the correlator is configured to process the pulses based on a discovery of the transmitter node, wherein the discovery is based on the signals which are based on the Doppler null steering.
 10. The system of claim 8, wherein the correlator is configured to process the pulses based on the time synchronization, wherein the time synchronization is based on the signals which are based on the Doppler null steering.
 11. The system of claim 8, wherein the correlator is configured to process the pulses based on a time period separating the pulses.
 12. The system of claim 11, wherein the time period is a predetermined time period configured to be known by the transmitter node and the receiver node prior to the transmission of the signal
 13. The system of claim 8, wherein the correlator is a single correlator.
 14. The system of claim 8, wherein the receiver node is configured to acquire a link to the transmitter node based on the processing of the pulses via the correlator.
 15. A system comprising: a transmitter node comprising: a communications interface comprising at least one antenna element; and a controller operatively coupled to the communications interface, the controller including one or more processors, wherein the controller has information of own node velocity and own node orientation relative to a common reference frame; wherein the transmitter node is time synchronized to apply Doppler corrections associated with the transmitter node's own motions relative to the common reference frame, wherein the transmitter node is configured to apply the Doppler corrections to signals using Doppler null steering along a plurality of Null directions based on the transmitter node's own motions, wherein the common reference frame is known to the transmitter node prior to the transmitter node transmitting the signals, wherein the transmitter node is configured to transmit pulses of the signals such that the pulses can be processed by a single correlator of a receiver node.
 16. The system of claim 15, wherein the correlator is configured to process the pulses based on a discovery of the transmitter node, wherein the discovery is based on the signals which are based on the Doppler null steering.
 17. The system of claim 15, wherein the correlator is configured to process the pulses based on the time synchronization, wherein the time synchronization is based on the signals which are based on the Doppler null steering.
 18. The system of claim 15, wherein the transmitter node is configured to transmit the pulses based on a time period separating the pulses.
 19. The system of claim 18, wherein the time period is a predetermined time period configured to be known by the transmitter node and the receiver node prior to the transmission of the signals.
 20. The system of claim 15, wherein the transmitter node is configured to acquire a link to the receiver node based on the processing of the pulses via the correlator. 